A highly sensitive Ag-graphene coated U-groove SPR-PCF sensor for early cancer detection

Abstract In this work, we theoretically propose a U-groove incorporated surface plasmon resonance based photonic crystal fiber (PCF) sensor for cancer diagnosis. The U-groove facilitates high plasmonic excitation as the plasmonic layer is closer to the core of the PCF. The U-groove is coated with silver (Ag) on which graphene is overlayered to support the field enhancement at the metal-dielectric interface. We optimize the various physical parameters of the proposed PCF sensor probe, namely, plasmonic metals (gold (Au)/Ag), Ag thickness, air hole radius, microslot depth, microslot width, pitch, and the thickness of the graphene to obtain the maximum sensitivity. Further, we analyze the significance of the graphene layer coating by comparing the sensitivity with and without graphene coating. Without graphene coating, the obtained wavelength sensitivities are 4750, 6000, 5071, 3650, 6857, and 7428 nm RIU −1 for the HeLa, PC12, Jurkat, Basal, MCF-7, and MDA-MB-231 cells, respectively. However, for 9-layer graphene coating, we obtain the wavelength sensitivities of 5666, 7214, 6000, 4300, 8500, and 9428 nm RIU −1 for the HeLa, PC12, Jurkat, Basal, MDA-MB-231, and MCF-7 cells, respectively. This corresponds to the enormous increase in the sensitivity of 19%, 20%, 18%, 17%, 24%, and 26% by using graphene as an overlayer. Besides, we also compute the amplitude sensitivities, wavelength and amplitude resolution, signal-to-noise ratio, figure of merit, and sensing length for the proposed sensor. To test the robustness of the sensor, we carry out the fabrication tolerance studies for a 5% variation from the optimized value of the PCF. The results corroborate that our sensor is highly tolerant against perturbations. To the best of our knowledge, the proposed sensor exhibits higher sensitivity than the other graphene-coated PCF sensors for cancer cell detection reported so far. Thus, we firmly believe that the proposed graphene-coated U-cut PCF sensor can be a potential candidate for cancer detection.